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CCS Oxyfueling cement kilns

CCS is a new technology, not yet proven at the industrial scale in cement production, but potentially promising. CO2 is captured as it is emitted, compressed to a liquid, then transported in pipelines to be permanently stored deep underground.

Cement is a global commodity, manufactured at thousands of plants. The industry is consolidating globally, but large international firms account for only 30% of the worldwide market. The principal and most visible market for cement is the construction industry in a multitude of applications where it is combined with water to make concrete. Most modern civil engineering projects, office buildings, apartments and domestic housing projects use concrete, often in association with steel reinforcement systems. In many developed countries, market growth is very slow, with cement used in bulk primarily for infrastructure construction, based on the Division of Technology, Industry and Economics of UNEP. In developing country markets (e.g. China), growth rates are more rapid. Because it is both global and local, the cement industry faces a unique set of issues, which attract attention from both local and international level.

One possible way to reduce CO2 emissions is via the Carbon capture and storage (see the ClimateTechWiki article on CCS). CCS is a combination of technologies designed to prevent the release of CO2 generated through conventional power generation and industrial production processes by injecting the CO2 in suitable underground storage reservoirs. Basically, capture technology separates CO2 emissions from the process, after which the compressed CO2 is transported to a suitable geological storage location and injected. Feasible methods of transporting of CO2 include both pipelines and shipping. Appropriate geological storage locations for CO2 include abandoned oil and gas fields, deep saline formations and unminable coal seams.

Introduction top

Manufacturing industries in general account for one-third of global energy use. Direct industrial energy and process CO2 emissions amount to 6.7 gigatonnes (Gt), about 25% of total worldwide emissions, of which 30% comes from the iron and steel industry, 27% from non-metallic minerals (mainly cement) and 16% from chemicals and petrochemicals production (IEA, 2008). Cement production involves the heating, calcining and sintering of blended and ground materials to form clinker (see Wikipedia clinker (cement)). As a result, cement manufacturing is the third largest cause of man-made CO2 emissions due to the production of lime (see Wikipedia lime mortar), the key ingredient in cement. Therefore, energy savings during cement production could lead to lower environmental impact.

One possible way to reduce CO2 emissions is via the Carbon capture and storage (CCS). CCS is a combination of technologies designed to prevent the release of CO2 generated through conventional power generation and industrial production processes by injecting the CO2 in suitable underground storage reservoirs. Basically, capture technology separates CO2 emissions from the process, after which the compressed CO2 is transported to a suitable geological storage location and injected. Feasible methods of transporting of CO2 include both pipelines and shipping. Appropriate geological storage locations for CO2 include abandoned oil and gas fields, deep saline formations and unminable coal seams.

There are several technologies that are employed in the capture, transport and geological storage of CO2. The majority of research and development has been directed towards efficiency improvements in the technologies used to separate CO2 from other compounds normally emitted by an industrial process. These technologies are generally referred to as ‘capture technologies’. Capture processes can be grouped in three categories, whereby the suitability of each approach depends on the industrial process or type of power plant in question: post combustion, pre combustion, oxyfuel combustion. A typical presentation of these processes can be found below.

illustration © climatetechwiki.org

Figure 1: CCS processes (Source: CO2CRC)

For the cement production, oxyfuel combustion is of importance for the reduction of CO2 from this sector. In this case, the primary fuel is combusted in oxygen instead of air, which produces a flue gas containing mainly water vapour and a high concentration of CO2 (80%). The flue gas is then cooled to condense the water vapour, which leaves an almost pure stream of CO2. Additional equipment is required for the in situ production of oxygen from air (Mckinsey & Company, 2008). In the Figure below a typical oxyfuel combustion process is presented.

illustration © climatetechwiki.org

Figure 2: Oxyfueling CCS process (Source: ECRA)

CCS is a new technology, not yet proven at the industrial scale in cement production, but potentially promising. CO2 is captured as it is emitted, compressed to a liquid, then transported in pipelines to be permanently stored deep underground. In the cement industry, CO2 is emitted from fuel combustion and from limestone calcination in the kiln. These two CO2 sources may require industry-specific capture techniques that are low-cost and efficient, and literature studies show that some capture technologies seem more appropriate for cement kilns than others (IEA 2009). CCS could capture between 85-95% of all CO2 produced (IPCC, 2005), but net emission reductions are in the order of 72 to 90% due to the energy it costs to separate the CO2 and the upstream emissions (Viebahn et al., 2007). Once CO2 has been effectively ‘captured’ from a process, it will be required to transport it to a suitable storage location. CO2 is most efficiently transported when it is compressed to a pressure above 7.4 MPa, and a temperature above approximately 31˚C. Under these conditions, the CO2 displays supercritical properties; it is a liquid with gas characteristics. Thus, CO2 would normally be transported at high pressures in pipelines made of carbon steel, not dissimilar to normal natural gas pipelines, or in ships if it needs to cross a great expanse of water. 

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Feasibility of technology and operational necessities top

Worldwide, there are currently four examples of full-scale CCS projects, all of them in the industrial sector and not in electricity production. In addition to Weyburn, which uses CO2 from a coal gasification facility in the United States, the Norwegian oil company Statoil has been injecting around a million tonnes of CO2, separated from natural gas, per year into deep saline formation under the North Sea since 1996, and since 2008 similar technology is applied in the Snohvit project, also in Norway. A consortium of BP, Statoil and Sonatrach have been injecting CO2 at In Salah in Algeria, also with CO2 originating from gas production. Technology similar to pre-combustion capture is used in fertilizer and hydrogen production, where the CO2 captured is used in other industrial processes, or vented. Oxy-fuel combustion technology for use in power generation is still in the demonstration stage but is currently tested in Germany by Vattenfall, a European electricity company. CCS technologies for the cement sector are viable when the full chain of CCS is available, including transport infrastructure, access to suitable storage sites, and a legal framework for CO2 transport and storage, monitoring and verification, and licensing procedures. As CCS requires CO2 transport infrastructure and access to storage sites, cement kilns in industrialised regions could be connected more easily to grids, compared to plants in non-industrialised areas.  

The global capacity to geologically store CO2 is large, with recent basin-wide potentials estimated between 8,000 Gt and 15,000Gt (IEA, 2008b). However, the level of knowledge concerning storage potentials varies on a global, regional and local scale (IPCC, 2005). Estimates of storage capacities are most advanced in Europe, North America, Japan and Australia. Depleted oil and gas reservoirs are estimated to have a global storage capacity of between 675-900 GtCO2, and this storage option appears suitable because of the existing knowledge of such locations, as well as the potential to re-use existing infrastructure from oil and gas extraction processes (IPCC, 2005). Deep saline formations are understood to have a storage capacity of at least 1000 GtCO2, and are believed to be distributed in many of the world’s sedimentary basins. It has been stressed that more information regarding storage capacities is required in areas experiencing accelerated growth in energy use, including China, India, Southeast Asia, Eastern Europe and Southern Africa (IPCC, 2005). 

illustration © climatetechwiki.org

Figure 3: Stages of maturity of CCS capture, transport and storage components ( IPCC, 2005)

Status of the technology and its future market potential top

The cement industry is already active in R&D for CO2 capture. Up to now, pre-combustion technologies have never been used in a cement plant. Oxy-fuel technology is a candidate for CO2 capture at cement kilns. There are experiences from cement kilns in the USA which were operated with oxygen enrichment (to increase the production capacity). Furthermore, oxy-fuel technology will be investigated at power plants in the next years, so that some of the results obtained may be transferred to cement kilns. Oxy-fuel seems to be applicable only at new kilns, because a retrofit at existing kilns would be too costly (ECRA 2007). Oxyfuel technology is now being demonstrated at small-scale power plants, so results obtained may be helpful to future cement kilns. From a technical point of view, carbon capture technologies in the cement industry are not likely to be commercially available before 2020 (IEA 2009).

According to the European Cement Research Academy (ECRA), in Russian experiments at laboratory and industrial scale oxygen was mixed in the primary air as well as in the secondary air. The impacts of the oxygen boosted caused a distinct shorter, tighter, brighter and hotter flame. In short-term tests with oxygen enrichment up to 35 % by volume an increase of 56 % kiln capacity was achieved. But due to higher thermal load problems with kiln refractory appeared. Also the energy sector has little experience with oxy-fuel technologies. The Swedish power company Vattenfall Europe plans the first pilot plant with oxy-fuel technology for power generation. The horizon of commercial implementation of oxy-fuel technology is estimated to be around the year 2020 (ECRA 2007). Currently the Verein Deutscher Zementwerke e.V. is preparing a research project, which should provide the necessary basics to evaluate the key parameters of the oxy-fuel technology. 

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How the technology could contribute to socio-economic development and environmental protection top

The level to which CCS supports sustainable development is a widely debated topic. The discussions around allowing CCS into the Kyoto Protocol’s Clean Development Mechanism exemplify the varying opinions between stakeholders. It is argued by some that no technology involving the combustion of fossil fuels can be associated with sustainable development, due to the finite nature of such resources. Others point towards the effects of fossil fuel use, beyond emissions of CO2 alone, including the environmental impacts of coal mining (Coninck, 2008).

Contribution of the technology to economic development (including energy market support) top

An important benefit of enhancing energy efficiency in the cement industry would be the reduction in energy costs. Broadly speaking, in the EU cement industry the energy bill represents about 40% of total production costs, while European cement production techniques are amongst the most energy efficient in the world. Since the 1970s, in Europe the energy required for producing cement has fallen by about 30% and the scope for further improvements has became rather small.

Climate top

As stated above, CCS could capture between 85-95% of the CO2 produced in a plant (IPCC, 2005), but net emission reductions are in the order of 72 to 90% due to the energy it costs to separate the CO2 and the upstream emissions (Viebahn et al., 2007). According to the IEA (2009), A rough estimation, based on 10-20 large kiln projects globally (average 6,000 tonnes per day) and a reduction efficiency of 80%, would lead to an overall CO2 emission reduction of maximum 20-35 Mt per year.

Financial requirements and costs top

Although the concentration of CO2 in the exhaust gas makes cement CO2 capture an attractive proposition when compared to power generation, economies of scale make it more expensive. A single 2GW coal fired power station emits approximately the same amount of CO2 as the whole of the UK cement industry (MPA Cement 2009). According to the IEA (2008), the CCS for cement kilns costs around 200 USD/t CO2 and with a learning rate of 5% it needs to reach a cost of 75 USD/tCO2 to become commercially viable in the market. More in detail, some cost estimations for a carbon capture process for a 2 Mt per annum clinker plant reveal that in 20 years ahead (2030), almost 100-300 M E are required, with operational costs ranging from 10-50 E/ tonne of clinker. For both CCS technologies, these costs are considerable as they double for the post-combustion option and increase by 25% for oxy-combustion compared to non-CCS plant. Globally, the CCS technologies for cement kilns during their phases of demonstration (2015-2030)  and commercialization (2030-2050), can gradually reduce their saving costs from 150 - 75 USD/tCO2, while the annual CO2 reduction can increase from 0-0.25 Gt CO2/year in the initial phase to 0.4-1.4 Gt CO2/year in the full deployment phase of the CCS technology. The use of CCS in cement kilns would, however, raise production costs by 40% to 90%. For chemical or physical absorption systems, the cost would be approximately USD 50 to USD 75 per tonne of clinker, or USD 75 to USD 100 per tonne of CO2 captured. This cost comprises 40% capital cost, 30% cost for the heat, and 30% for transportation and storage. Still, the construction of a pipeline network entails a considerable capital investment, for instance for 5 million t/year throughput with a length of 100 km, the total cost for transportation amounts to 0.8-3.1 E/tCO2. The storage costs vary between 0.15 and 22.3 €/t CO2 – depending on the storage site (ECRA 2007). Different process designs using oxyfueling or chemical looping might halve the cost, but these are still in a conceptual stage.

References top

Coninck, H.C.De, 2008. Trojan horse or horn of plenty? Reflections on allowing CCS in the CDM. Energy Policy 36, pp. 929-936. 

ECRA (European Cement Research Academy), 2007. Carbon Capture Technology - Options and Potentials for the Cement Industry. Technical Report 044/2007. 

European Commission, 2009. Communication from the Commission to the European Parliament and the Council. Demonstrating carbon capture and geological storage (CCS) in emerging developing countries: financing the EU-China Near Zero Emissions Coal Plant project. Brussels, Belgium.

IEA, 2008a. Energy technology perspectives 2008 - Scenarios and Strategies to 2050. IEA/OECD, Paris, France.

IEA, 2008b. CO2 capture and storage: A Key Abatement Option, IEA/OECD, Paris, France.

IEA, 2009. Technology roadmap – carbon capture and storage. International Energy Agency, Paris, France. Available at: http://www.iea.org/papers/2009/CCS_Roadmap.pdf

IEA, 2010. Energy Technology Perspectives - Scenarios and Strategies to 2050. International Energy Agency, Paris, France.

IPCC, 2005. Special report on carbon dioxide capture and storage. Metz, B., Davidson, O., Coninck, H.C.De, Loos, M. and Meyer, L.A. (eds.). Cambridge University Press, Cambridge, United Kingdom and New York, USA, pp. 442.

Viebahn, P., Nitsch, J., Fischedick, M., Esken, A., Schuwer, D., Supersberger, N., Zuberbuhler, U. and Edenhofer, O., 2007. Comparison of carbon capture and storage with renewable energy technologies regarding structural, economic, and ecological aspects in Germany. International Journal of Greenhouse Gas Control 1 (1), pp. 121-133.